In the process of spinning yarn, a carding machine comes second in the sequence of spinning processes. Carding is undertaken mainly to disentangle fibers, intensively clean fibers by removing impurities and short fibers and to form a sliver to facilitate further processing. A prior art carding machine is illustrated in FIG. 1 together with an enlarged side view of a revolving flat in FIG. 1A. The carding machine mainly comprises three rotatable cylinders of different sizes and known as the licker-in 1, the main cylinder 2 and the doffer 3. A number of revolving flats 4 are mounted to travel around an endless path 5 positioned above the main cylinder 2. A saw tooth wire 6 is wound on to the surface of the main cylinder to form closely packed coils, so that the teeth extend radially from and substantially cover the circumferential surface of the main cylinder 2. The other cylinders are similarly wound with a saw toothed wire.
Wire staples are pressed through a flexible foundation to form the fine flexible wire teeth 4b of a flat top. Each flat top is mounted on a flat bar 4d known as a “bare flat” to form a “revolving flat 4” covered with the fine flexible wire teeth 4b. The end 4c of the wire projecting from the flexible foundation is bent in the intended direction of motion of the revolving flats. The tip of each tops wire is ground to a point. The path of the revolving flats 4 envelopes a part of the circumferential surface of the main cylinder 2 so that during the processing the material passes through a small gap between tops wire points and the teeth projecting from the main cylinder 2. The circumferential area of the main cylinder 2 covered by the revolving flat 4′ is known as the carding area. The angular direction of the wire points on the main cylinder 2 and the wire points on on the revolving flats are always kept opposite to each other in the carding area, so as to perform the carding action.
During processing of fibers in the carding machine, fibers are taken from a feed in small tufts by the licker-in 1. These tufts subsequently get transferred onto the main cylinder 2 in the form of a fine fleece. This fine fleece of fibers undergoes carding action between the teeth on the main cylinder and the revolving flats. During this intensive opening and cleaning operation the revolving flats being flexible start getting clogged with debris and the short fiber present in the fine fleece. Normally the revolving flats move in the same direction as that of main cylinder 2. As each revolving flat 4′ moves out of the carding area it is cleaned, so that a clean revolving flat 5 can re-enter the carding area to perform consistent carding action.
It has been observed that when the direction of the movement of the revolving flat is opposite to that of the main cylinder better carding action takes place. Hence this arrangement known as a “reverse flat movement system” is incorporated in the latest generation of high production cards. The fibers thus carded are collected by the doffer 3, which are later taken away to form a sliver.
As the extent of cleanliness of the revolving flats greatly influences consistent carding action, different types of cleaning system both mechanical and manual are in use. Different types of flat top cleaning mechanisms are provided by carding machine manufacturers to remove the short fibers deposited on the surface of the revolving flats and impurities clogged in the flat tops in the form of a fleece called flat strips.
The cleaning problem is more accentuated in cards with a reverse flat movement mechanism. The market demand to improve the carding process and its production leads to a demand for the use of a reverse flat movement and other improvements in the machine. However, existing revolving flat cleaning devices do not operate satisfactorily on a reverse flat movement mechanism.
With the processing of materials in the carding machine the tips of the wires in the revolving flats start wearing. To maintain consistent quality output the wire points must be reground. During the grinding process the worn out portion in the flat wire tips are cut off to provide a sharp front edge on the wire points for effective carding.
Conventionally a roller covered with either emery fillet or a full width grinding stone is used to undertake the grinding operation of flat tops. When flat tops are ground using conventional grinders there is always an increase in the land area on the wire tip. This increase of land area becomes more prominent with subsequent grindings. The increase of land area causes deterioration in the efficiency of the tops due to reduced holding capacity of fibers by the wire tops.